It is generally known that mechanically stabilized earth (MSE) includes soil with artificial reinforcing. The MSE structures are used for retaining walls, bridge abutments, dams, seawalls, dikes, and the like, as illustrated by way of example with reference to FIG. 1. Although MSE structures have been used throughout history, MSE was developed in its current form in the 1960s. The reinforcing elements used vary but generally include steel and geosynthetics. As applied for reinforcing dwellings, dikes and levees, and many structures to prevent erosion of soil, modern use of soil reinforcing for retaining wall construction was first pioneered by French architect and engineer Henri Vidal. The first MSE wall build in the United States was done so in 1971 on State Route 39 near Los Angeles. It is estimated that since 1997, many more than 23,000 MSE walls have been constructed in the world.
Originally, long steel strips 50 to 120 mm (2 to 5 in) wide were used as reinforcement. These strips are sometimes ribbed, although not always, to provided added resistance. Sometimes steel grids or meshes are also used as reinforcement. Several types of geosynthetics can be used including geogrids and geotextiles. The reinforcing geosynthetics are typically made from high density polyethylene, polyester, and polypropylene. These materials may also be ribbed and come in varying sizes and strengths.
By way of further background and with reference to “Mechanically Stabilized Earth Wall Inspector's Handbook,” State of Florida, Department of Transportation, Sep. 14, 2000, the disclosure of which is herein incorporated by reference in its entirety, established procedures for the construction of an MSE wall system. For example, during preparation of a site, the MSE wall footprint area including the zone of the wall facing, soil reinforcement and select backfill must be prepared. The foundation for the structure is graded level for a width at least equal to the length of soil reinforcement. Any soft or loose material that is encountered is stabilized. The wall system may comprise original ground, concrete leveling pad, wall facing panels, coping, soil reinforcement, select backfill, and any loads and surcharges. All of these items have an effect on the performance of the MSE wall and are taken into account in the stability analysis. A change in any of these items could have a detrimental effect on the wall.
For MSE wall installation, once the area has been properly prepared, a concrete leveling pad is typically poured in place. Coping is used to tie in the top of the wall panels and to provide a pleasing finish to the wall top. The coping can be cast-in-place or prefabricated segments. A filter fabric is typically used to cover the joint between panels, and is typically placed on the backside of the panels. This keeps the soil from being eroded through the joints and allows any excess water to flow out. Random backfill may be allowed in normal embankment construction. Select backfill meeting the gradation, corrosion, unit weight, internal friction angle and any other requirements of the specifications will typically be used. Soil reinforcement will be used to hold the wall facing panels in position and to provides reinforcement for the soil. The reinforcement can be made of steel (inextensible materials) or polymers (extensible materials). Wall panel spacers are used and are typically ribbed elastomeric or polymeric pads inserted between the panels. The panels or panels are used to hold the soil in position at the face of the wall and are typically formed in concrete but they can be metal, wood, block, mesh or other material.
The present disclosure is directed at least partially to the coping, which can be required to meet stringent barrier requirements depending upon placement of use. As generally described in the above referenced MSE Wall Inspector's Handbook, precast or cast-in-place coping barriers may be used. For precast units, a leveling course of concrete is placed prior to setting the units in place as illustrated with reference to FIG. 2. This provides the vertical control needed for installation of the coping. Precast barriers are typically tied together and strengthened against vehicle impact by a slab cast typically in 30-foot sections as illustrated with reference to FIG. 3.
By way of further example regarding needs in the industry, the use of one full precast traffic barrier (FPTB) positioned on a top of an MSE wall was discontinued by the Florida Department of Transportation (FDOT) and the Federal Highway Administration (FHWA) because the typical structure did not meet impact loading criteria established by the FHWA. By way of example, where previously a barrier needed to withstand being hit be an automobile traveling at 55 mph, current regulations require the ability to withstand a head-on impact by a truck traveling at 65 mph.
Therefore, it is readily apparent that there is a need for an improved FPTB and MSE structure that can meet current impact criteria on FDOT projects and still enable the cost and time efficient installation of a precast barrier. It is to that purpose the following embodiments are herein disclosed.